Research On The Test Of Strand Residual Prestress Of Prestressed Concrete Beam

Prestress has reinforced concrete structure crack later or not crack completely, which is the prestressed concrete structure new concept. Then, the prestress value has been becoming people concerning focus. The prestress is different at different time since the prestress is imposed. The concept of residual prestress is come up with based on this situation. The current calculation method for residual prestress, classify prestress loss method, is discussed according to the residual prestress concept, the residual prestress of test structures were calculated by current code's "classify prestress loss method".Test and research data show that the current code's "classify prestress loss method" calculation results are not all exact. If these results are used to predict the security of the structure, the prediction may be not correct, or the prediction may lean towards danger. The residual prestress was tested follow up the scent from steel tensed to the end of curing period. The following conclusion is attained from analysis of the test data: the residual prestress of the structures is reducing in curing period, which reduces fast at prophase, and slow in anaphase, and reduces according to minus logarithm rule.Load effection on the residual prestress is studied. The result reveals that loading does not result to reduce of residual prestress. On the contrary, short-term loading results to little increase of the residual prestress, because concrete creep as well as deforms elastically. short-term load doesn't speed up the loss of prestress; on the contrary, it reduces the speed of prestress loss in the strands.Naturally, people can get the residual prestress value from its rule, but exploring it needs many test researches and engineering practice. If the existing structure residual prestress can be measured by some measurement method, the method will be valuable for engineering. Therefore, the principle of ultrasonic method and vibration method is discussed from the theory point view, holing method and flexivity method is studied based on theory and test.Dynamics analysis reveals that the more residual prestress it has, the less natural frequency it has when eccentricity is not changed. While dynamics test is opposite to the rule, in other words, the natural frequency becomes more with the increment of residual prestress. According to analysis, that existing of residual prestress has revised the structure's stiffness is inferred. Ultrasonic method measuring stress has widely applied in measurement of bolt stress, which implies people that it is possible to use to ultrasonic method to measure residual prestress. The basic principle of ultrasonic method measuring residual prestress is introduced, and the correlation of residual prestress and longitudinal and transversal wave time is derived and analyzed in detail. Measurement device diagram is also designed in this paper.Theory analysis and finite element calculation for holing method show that the residual prestress is able to measured by holing method as long as the hole diameter, hole depth and measuring location is appropriate. Average value of test data is near to the finite element calculation results, while the data's variance is too much.Flexivity method which depends on residual prestress and stiffness correlation is a practical measurement method. The following results can be concluded from static load test of three prestressed concrete beams: the prestressed structures stiffness is different from the stiffness presented in the current code, and the more residual prestress it has, the more stiffness it has, the less residual prestress, the less stiffness. The correlation of residual prestress and stiffness is attained by regression method in this test.This research is a comprehensive process of theory analysis and test analysis. The theories used in this paper are mellow and complete. Some test destination is to confirm feasibility of theory measurement method, and most to explore new rules. The experienced formula in this paper which is only come from the test structures is not perfect enough and need much more scientific experiment and engineering practice to complement and modify.